Computer assisted surgery systems (CAS systems) or image guided surgery systems that are provided with a computer and a position measurement device in order to measure the position of surgical instruments, devices and a body portion of the patient are often used to perform minimally invasive surgery. Computer assisted surgery systems (CAS-systems) are disclosed e.g. in EP 0 359 773 to Schlöndorff, U.S. Pat. No. 5,383,454 to Buchholz and in U.S. Pat. No. 5,682,886 Delp. CAS systems may comprise a memory means to store medical images such as e.g. X-rays, computertomographs or MR images (magnetic resonance images). Thereby the medical images may be gathered pre-operatively or intraoperatively.
Computer assisted orthopaedic surgery systems include a) CT based systems, which may use a preoperative CT (Computertomogram) of a bone or bone fragment to establish a three-dimensional anatomical model that is referenced with the intraoperative respective bone or bone fragment through landmark based or surface based registration or matching; b) CT based and fluoroscopy systems, which use the same method as CT based systems to establish a three-dimensional anatomical model, whereby the preoperative CT of a bone or bone fragment is registered or matched to the intraoperative respective bone or bone fragment through using a surface model of the bone or bone fragment and its projections in the planes of the fluoroscopic images; and c) fluoroscopy based systems, which use calibrated fluoroscopes to generate undistorted images of a bone or bone fragment and virtual geometric representations of the projection of surgical tools.
A method of generating tomographic images of a body using penetrating radiation is known from EP 1004272 to Lin. This known method comprises the steps of a) cycling the radiation source among a plurality of positions relative to the region of interest of the body such that radiation from the radiation source passing through each of a plurality of focal planes, which are parallel to the detector plane and within the region of interest, impinge upon the detector plane superimposed and offset from each other; b) shifting the electronic views for a first selected focal plane, such that the radiation which passes through each incremental element of the first selected focal plane contributes to a common pixel of the electronic views; and c) finally, summing the electronic views such that the pixels of each electronic view corresponding to the incremental element on the first selected focal plane are summed to generate a slice image taken through the first selected focal plane.
Known methods have the disadvantage that CT-scanning delivers cross-sectional images of the patient body whereas fluoroscopic X-ray images deliver two-dimensional images and, therefore, many X-ray images are required in several parallel planes and under several different angles of the radiation source to obtain a three-dimensional model.
The present invention provides a virtual three-dimensional representation of a bone or bone fragment, which representation may be based on two-dimensional images such as fluoroscopic images. Accordingly, the present invention may advantageously allow representations with reduced radiation exposure to the patient and less invasive surgical operations.